Semiconductor devices, such as printed boards and plastic packages, are manufactured using metallized boards that are known to be fabricated by pattern formation using photosensitive dry films.
As indicated generally by numeral 1 in FIG. 1, a photosensitive dry film consists of a support film 2, a photosensitive resin layer 3 and a protective film 4 that are placed one on another to form an integral unit.
To apply the photosensitive dry film 1, the protective film 4 is peeled off and the photosensitive resin layer 3 is thermally compressed to a substrate (not shown). Then, being covered with the support film 2, the photosensitive resin layer 3 is selectively exposed. After the exposure, the support film 2 is peeled off and development is performed such that the unexposed areas of the photosensitive resin layer 3 are selectively removed to form a photosensitive resin pattern (photoresist pattern).
In the next step, with the photoresist pattern being used as a mask, the substrate is etched or those areas between adjacent elements of the photoresist pattern are plated or otherwise processed, followed by removing away the photoresist pattern to form a desired metallization on the substrate.
Since the photosensitive dry film is stored for a long period with the protective film adhering to the surface of the photosensitive resin layer, the photosensitive resin composition (the principal component of the photosensitive resin layer 3) must first be capable of withstanding prolonged storage. Other performance requirements include high enough resolution to enable the formation of fine-line photoresist patterns that are adaptive to the recent microfabrication technology, good adhesion to the work and high resistance to plating. In addition, in the manufacture of today's semiconductor devices such as printed boards and plastic packages which are seeing a growing reduction in feature size, etching is predominantly performed by dry processes using CF4, CHF4, He and other gases. Therefore, the photosensitive dry film is also required to have resistance to the hostile environment of dry etching.
Conventional photosensitive resin compositions that can be used in photosensitive dry films are described in JP 52-99810A and other patents.